|Sony Alpha standard prime lenses
Standard lenses are so-called because they match the magnification of the human eye. As such they produce very natural-looking results and are ideal general-purpose models. The standard focal length for film and full-frame DSLRs is 50mm and before the widespread adoption of zoom lenses, almost every photographer owned one.
Like most fixed focal length lenses, standard 50mm models generally have a much brighter aperture (smaller f-number) than zoom lenses, allowing them to gather more light and be more flexible in low light conditions. These smaller f-numbers also allow you to more easily blur the background on portraits.
Lenses with f-numbers smaller than f2 are normally very expensive, but 50mm models are the exception. Due to their ease of construction and high manufacturing volumes, 50mm lenses with very bright apertures can be very affordable – and models with f1.8 or f1.4 apertures are most common. To put these numbers in perspective, most kit zoom lenses at around 50mm have an aperture of f5.6. A lens with an f1.4 aperture can actually capture 16 times more light. This low light performance also makes them great for astro-photography.
As always, bear in mind any reduction in field due to your DSLRs sensor when choosing a lens. Sony’s APS-C models like the A100, A200, A300, A350 and A700 have a reduction factor of 1.5x, which effectively turn 50mm lenses into 75mm models. So if you want 50mm standard coverage on one of these models, you should be considering actual focal lengths closer to 35mm.
That said, an equivalent of 75mm gives you short-telephoto coverage which is ideal for portrait work, especially with the small f-numbers allowing very blurred backgrounds. As such, 50mm lenses are proving very popular with DSLR enthusiasts.
Note the Sony DT 50mm f/1.8 SAM lens is not compatible with full-frame bodies.
For a full explanation of lens specifications and examples of coverage at different focal lengths, check out our Camera Labs Lens Buyers Guide.